Conversion of hydrocarbons



Patented Mar. 26,

convrzasron or nrmtoosnnons John F. Sturgeon, El Dorado, Arln, assignorto Universal Oil Products Company, Chicago, Ill., a corporation ofDelaware No Drawing. Application June 18, 1943, Serial No. 491,391

12 Claims. (01. zoo-683.3)

This is a continuation-in-part of my co-pending application, Serial#433,442, filed March 5, 1942, now United States Patent 2,335,550 issuedNovember 30, 1943, which in turn is a continuation-in-part ofapplication, Serial #293,923, filed September 8, 1939, now United StatesPatent 2,278,223 issued March 31, 1942.

This invention relates to the treatment of hydrocarbons to producetherefrom less-saturated hydrocarbons containing the same number ofcarbon atoms but a smaller number of hydrogen atoms per molecule. In amore specific sense, the invention is concerned with a process fordehydrogenating aliphatic hydrocarbons.

Parafiinic hydrocarbons, which are present in considerable amounts innatural gases, casinghead gases, cracked gases, etc., and which arefrequently used only as fuel, are convertible into more usefulunsaturated hydrocarbons by dehydrogenation in the presence of catalystshereinafter set forth. Butenes and higher olefins are converted intodiolefins, and normally liquid parafiinic hydrocarbons are transformedinto more useful olefinic and diolefinic products by catalyticdehydrogenation.

In a broad aspect the present invention comprises a hydrocarbonconversion process wherein hydrocarbons are reacted at conversion conditions in the presence of a catalyst which at some stage in itsmanufacture has a component or components existing as a gelatinoushydrogel, which hydrogel has been subjected to freezing and thawing todestroy its gelatinous structure.

In one embodiment the present invention comprises a process fordehydrogenating aliphatic hydrocarbons in the presence of a catalystprepared by forming a hydrogel of a metal oxide, freezing and thenthawing said hydrogel to destroy its gelatinous structure and to convertit into a finely divided powder, and compositing with said powder atleast one additional catalytic substance such as a metal oxide to form acomposite dehydrogenating catalyst.

In a more specific embodiment the present invention comprises a processfor dehydrogenating aliphatic hydrocarbons in the presence of a catalystformed by precipitating an alumina hydrogel by the addition of a base toan aqueous solution of an aluminum salt selected from the groupconsisting of the chloride, nitrate and sulfate, sufiiciently freezingand then thawing said hydrogel to destroy its gelatinous structure andto convert it into a substantially amorphous and nongelatinous powderand an aqueous solution, removing a major proportion of said aqueoussolution from said powder, washing the powder to remove water-solubleimpurities, and mixing the powder witha solution of a metal compoundunder conditions to impregnate the powder with the 'oxide of said metal,heating to remove water, drying the'composite, forming, and calcining toproduce an active dehydrogenating catalyst.

The catalysts employed in the process of the present invention haverelatively higher dehydrogenating activities than those previouslyprepared from the same starting materials by methods not involvingfreezing and thawing of hydrogels as herein set forth. The essentialfeature of the present invention is the use of catalyst compositescontaining a component prepared by freezing and thawing hydrogels orhydrous oxides to eliminate water and then utilizing subsequent stepsinvolving washing to remove impurities, forming, and calcining toproduce formed particles or powdered catalyst of high dehydrogenatingactivity.

An advantage of utilizing freezing of a hydrogel during the preparationof dehydrogenating catalysts is that the frozen and thawed material maymore easily be washed substantially free from impurities such as alkalimetal compounds than is possible when washing the original hydrogels.Furthermore, grinding of the frozen, thawed, purified and driedcomposite is frequently unnecessary before forming it into catalystparticles; and several drying and screening operations are avoided whichmust ordinarily be made when removal of impurities from precipitatedhydrogel catalysts is effected mainly by washing. Also'the apparentdensity of a catalyst prepared from a frozen hydrogel composite is lessthan that of a similar catalyst prepared from the same kinds ofhydrogels which have not been frozen impurities. The term apparentdensity is used in reference to the ratio of the weight of unit grossvolume of catalyst to the weight of an equal gross volume of water.

The hydrogel or hydrous oxide which is subjected to the freezingandthawing treatment in accordance with the preferred embodiment of thepresent invention has relatively low dehydrogenating activity in itselfand thus may comprise the hydrous oxides of aluminum, magnesium, zincand cadmium. When these oxides are present with other oxides in complexcomposites, the materials of relatively low dehydrogenating activitiesare commonly looked upon as carriers, supports, or spacing agents,although they sometimes exhibit specific promoting effects which are notexactly in accord with their individual activities in such reactions.Alumina hydrogel is particularly suitable for treatment in accordancewith the present invention and therefore is preferred.

The exact conditions which are optimum for the freezing treatment of thegels, such .as temperature and rate and time of freezing, are dependentupon the composition of the gel in question, its water content, andother factors. During freezing, the hydrogel composite loses its gelstructure so that the thawing of the frozen material produces an aqueoussolution and a fine powder or granular material, the latter beingreadily separable from the aqueous solution. The solid powdered materialso'obtained by the thawing of the hydrogel may then be washed with waterto remove water-soluble impurities and then dried, or preferably thepowdered material may be dried, washed, and again dried. If desired, thepowdered material may be ground further and formed into particles byextrusion, pelleting, or other similar methods with or without theaddition of promoters prior to the particle-forming operation- Thepelleted, otherwise formed, or powdered catalytic material is thencalcined at a temperature from about 900 to about 1500 F. to produceactive catalyst.

The other component or components having a higher dehydrogenatingactivity than alumina, for example, and which are composited .with thealumina, include compounds and particularly the oxides of the followingelements: titanium, zirconium, and thorium in the left-hand column ofgroup IV of the periodic table; silicon and tin in the right-hand columnof group IV; va-

nadium, columbium, and tantalum in the lefthand column of group V;chromium,.molybde-' num, and tungsten in the left-hand column 01 groupVI; and iron, nickel, and cobalt constituting the fourth series of VIII.

Since substantially all of the oxides of these elements arealternatively utilizable in produce ing catalyst composites havingdehydrogenating activities, it is readily'seen that a considerablenumber of alternatively utilizable composite materials can be produced,although obviously the catalytic activities of the difierent possiblecom posites will not be exactly equivalent, particularly whendehydrogenating different hydrocar-'.

bons which may thus be converted into'other hydrocarbons having the samenumber; ot'carbon atoms but a smaller number of hydrogen atoms permolecule. Some of the oxides of these elements possess greaterdehydrogenating activi'-' ties than others, and some of the materialsproduced by the reduction of the oxides have great-' which may becalcined to produce active dehydrogenating catalysts.

' According to one method of preparation a precipitated alumina hydrogelis prepared by addition of a base to an aluminum salt, as the chloride,nitrate, or sulfate, or precipitated alumina hydrogel is formed bytheaddition of an acid such as hydrochloric or sulfuric, or'of asolution of an aluminum salt, to a sodium aluminate solution. Aluminahydrogel so formed is frozen and then thawed so as to break down the gelstructure, producing hydrated aluminum' oxide in powdered form, which isseparated from mechanically removable water, washed to removewater-soluble impurities, and dried. It is preferable to precede thewashing step by drying treatments. The finally dried powder is thenimpregnated with a solution of chromic acid dissolved in water, and thedesired quantity of magnesium oxide is then added to the impregnatedpowder. The resultant composite of hydrous aluminum oxide and compoundsof chro-- mium and magnesium is then dried and calcined; or dried,formed into particles, and calcined.

According to a second method, hydrated aluminum oxide is prepared byprecipitation, and the hydrogel is frozen and then thawed, washed, and

dried as in the first method. Then the hydrated aluminum oxide isactivated by being calcined at a temperature between about 900 and about1500? F. to produce activated alumina which is impregnated with chromicacid solution and the desired amount of magnesium hydroxide is addedthereto.

The process of freezing precipitated hydrogels is applicableparticularly to the preparation of dehydrogenation catalysts, such asaluminachromia and alumina-chromia-magnesia, and may be used also in thepreparation of any other catalyst which may be produced in the form ofaprecipitated hydrogel which requires washing to remove water-solubleimpurities therefrom. Thus the freezing and thawing operations utilizedin the production of the preferred dehydrogenation catalyst of thepresent invention may be applied to substantially any type of catalyticmaterial which exists as a hydrogel during one phase of its manufactureand requires repeated washed with water and aqueous solutions to removedeleterious impurities.

- It is usually good practice in the final steps ofpreparation ofdehydrogenation catalyst composites to calcine them at a temperaturebetween about 900 and about 1500 F. Such calcination treatment does notcause complete dehydration of the hydrated oxides, but gives catalyticmaer activities than their oxides as is the case with: iron, nickel, andcobalt. The oxides of chromium, molybdenum, tungsten, and vanadium all"have outstanding activities in reactions involving the directdehydrogenation of aliphatic hydrocarbons including particularlyalkanes, alkenes, and arylalkanes, although in this group of oxidesthere are variations in activities with different hydrocarbons. Theoxides of silicon, titanium, zirconium, cerium, and thorium usually havelower dehydrogenating potency than those of chromium, molybdenum,tungsten, and

vanadium and among themselves, cerium is usually highest in activity.

In preparing dehydrogenation catalysts oi the alumina-chromia-magnesiatype, alumina may be composited and mixed with chromia and magnesia inseveral ways to form composites terials of good structure and porosityso that they are able to resist for a long time the deterioratingeffects of the. service and reactivation period to which they aresubjected.

The dehydrogenating value of different composites and the activity ofcomposites having different proportions of oxide'ingredients have beenfound to vary considerably with the methods of preparation ofthe-composites. In the case of alumina-chromia-magnesia' catalysts themost efl'ective and economical proportions comprise major amounts ofalumina and relatively minor amounts oi chromia and magnesia; while inother cases best results are obtained when employing catalystscontaining major amounts of catalyst components having relatively highdehydrogenating activities and minor amounts of oxides having relativelylow catalytic activities such as alumina, magnesia, zinc oxide, andcadmium oxide.

In carrying out the dehydrogenation of various hydrocarbons according tothe present process, a solid composite catalyst in the form of particlesof graded size or small pellets and preparedas hereinbefore set forth,is used as a filler in reaction tubes, reactors, or chambers and thehydrocarbon to be dehydrogenated is passed through the catalyst afterbeing heated to the proper temperature which is usually between about750 and about 1400 F., although more commonly between about 900 andabout 1200 F. The catalyst reactors may also be heated exteriorly tomaintain the proper temperature for the reaction which- As analternative mode of operation using dehydrogenating catalysts of thecharacter herein set forth, they may be employed in finely dividedcondition in stationary or moving masses through which the vapors of thehydrocarbons are passed. Such operations may be conducted so that thereis relatively little mechanical loss of catalyst from the reaction zonebecause of the carrying action of the reactant streams, or the rate offlow of vapors may be adjusted so that definite amounts of powderedcatalyst are carried from the reaction zone and later separated from thetreated vapors and reactivated by suitable treatment with anoxygen-containing gas mixture.

In this specification and in the claims, the term aliphatic hydrocarbonsis used in referring to alkanes, alkenes, and arylalkanes which areconverted into more unsaturated hydrocarbons in the presence of thedehydrogenating catalysts herein described. Under the operatingconditions also herein set forth the aliphatic hydrocarbons losehydrogen from the carbon chain of the respective hydrocarbons. Undersome circumstances the addition of steam to the hydrocarbon undergoingdehydrogenation, particularly in the case of hexane and higherhydrocarbons, is favorable to the production of olefinic hydrocarbons.

The time of contact employed will vary with the activity of the catalystused, the temperature employed, and the hydrocarbon or hydrocarbonmixture undergoing treatment. The relatively low molecular weightparaffins such as ethane and propane are generally more difficult todehydrogenate than the higher normally gaseous and liquid paraflins.Paraflinic hydrocarbons frequently require a higher catalyst temperatureor longer time of contact than do the corresponding olefins which areconvertible into diolefinic hydrocarbons by dehydrogenation, saiddiolefin formation being carried out generally at a subatmosphericpressure. Productionof arylalkenes by catalytic dehydrogenation ofethyl-benzene or other alkylated aromatic hydrocarbons having at leastone ethyl group or higher alkyl group, is preferably carried out at arelatively high temperature by use of a shorttime of contact in thepresence of the catalyst and under a reduced pressure in order to obtaina relatively high yield of desired product without excessive hydrocarbondecomposition andrapid decrease in catalyst activity due tocarbonization.

Since the usual method of operating commercial dehydrogenation plants isto utilize several catalyst reactors, each containing at least one fixedcatalyst bed, connected in parallel so that one reactor may be utilizedin dehydrogenating a hydrocarbon charge while the catalyst in the otherreactor is being reactivated, as by heating" in an oxygen-containinggas, itis preferable to so balance conditions in the two parts of thecycle that the times of processing and reactivation are substantiallyequal. A further problem to be solved by trial is the question of thelength of the operating cycle, since best overall results are usuallyobtained in continuous plants when operations are conducted forrelatively short intervals followed by a correspondingly short time ofreactivation rather than by allowing the catalyst particles to becomecontaminated excessively by carbonaceous deposits.

Products from the catalytic reactors are subjected to suitable treatmentto remove therefrom the hydrocarbons formed by dehydrogenation, whilethe unconverted hydrocarbon material is recycled to further contact withthe catalyst. For example, olefinic or diolefinic materials resultingfrom dehydrogenation of paraffins, olefins, or alkylated aromatichydrocarbons may be subjected to polymerization in the presence ofsuitable catalysts or they may be treated directly with chemicalreagents to produce other desirable and commercially valuablederivatives. After the most reactive products have been removed, theresidual materials are then recycled for further treatment with orwithout complete removal of hydrogen.

Many of the composites included in the present types of catalysts areselective in removing two hydrogen atoms from a paraffin molecule toproduce the corresponding olefin without furthering to any great extentundesirable side reactions. and because of this, there is an unusuallyhigh conversion of paraflins into olefins, as will be shown in theexample. When the activity of such a catalyst begins to diminish, it isreadily reactivated by the expedient of oxidizing with air or otheroxidizing gas at a moderately elevated temperature, usually within therange employed in the dehydrogenating reactions. This oxidationeffectively removes most of the carbonaceous deposits which graduallycontaminate the surface of the particles during the processing periodand decrease their efficiency. It is characteristic of such catalyststhat they may be reactivated repeatedly without substantial loss ofcatalytic efficiency.

When reactivating partly spent catalysts by oxidation with air or otheroxidizing gas mixtures, lower metal oxides are sometimes oxidized tohigher oxides which may combine to a greater or lesser extent with someof the other components in the catalyst mixture to form salts. Forexample, the oxide ClzOs is extensively oxidized to CrOs duringreactivation of the spent alumina-chromia catalyst with an oxidizing gasmixture and the chromium trioxide combines with alumina to form achromate. Later, this chromate. or the adsorption complex of ClOs onA1203 is apparently decomposed by contact with reducing gases in thefirst stages of service to reform the green sesquioxide CrzOa, and toregenerate the real catalyst and hence the catalytic activity.

In the dehydrogenation of butanes it has been found essential thatparticular conditions of operation be observed in order to producemaximum yields of butenes in the presence of aluminum oxide-chromiumsesquioxide catalysts of suitable activity. In regard to temperature,the optimum range is from about 1000 to about 1200-F., at the surface ofthe catalytic particles. It is essential, in combination with a suitablehourly space velocity'(volume of butane charged per hour per volume ofgross catalyst space), that this temperature be maintained within thisrelatively narrow range and that itbe measured in the catalyst mass at asufficient number of points so that the average temperature falls withinthis interval. It is customary in many commercial plants to measureinlet and outlet temperatures of catalyst chambers and to consider theaverage temperature to be the mean of these two. But this is notaccurate practice, since dehydrogenation reactions are endothermic andthe average temperature would not be represented by the mean of theinlet and outlet on account of the need for adding heat externally.

In using the above conditions of temperature, pressure, and time, aconversion per pass of butanes to butene of about 15 to 25 per cent ispreferably efiected, which, it has been found, corresponds to a minimumdeposition of carbon upon the surface of the catalyst and a minimum ofside reactions, such as would result in the formation of degradationproducts resulting from the scission of the carbon-to-carbon bonds. If atime of contact is maintained corresponding to a maximum once-throughyield of butenes (which may be as high as 50 to 60%) the deposition ofcarbon is greatly accelerated and demethanization and other splittingreactions rather than dehydrogenation occur, whereas when approximatelya 25 per cent conversion per pass is maintained it is possible toproduce ultimate yields of approximately 95 per cent of butenes byrecycling of unconverted butane. Further, it has been determined that indehydrogenation of butanes by the preferred catalysts, the rate ofcarbon deposition passes through a minimum within the temperature rangegiven. That is, if temperatures lower than about 1100 F. are employedand the time of contact is increased to obtain approximately 25 per centconversion per pass, a relatively large amount of carbon is depositedand similarly the rate of carbon deposition begins to rise markedly attemperatures aboveabout 1290 F. even though the time of contact isreduced to maintain only a 25 per cent conversion er pass.

The following example is submitted to show specific results obtained indehydrogenating bu.. tane in the presence of catalysts prepared bymethods involving the freezing and thawing of hydrogels, although thedata submitted are not intended to limit correspondingly the generallybroad scope of the invention.

Three comparative dehydrogenation catalysts were prepared so as to havecompositions corresponding to the molecular ratios of 30 A1203:3Cr203I2MgO. One of these composites was prepared by the usual method ofthe prior art comrising precipitating aluminum hydroxide from aluminumsulfate solution by the addition of aqueous ammonia, repeatedly washingto remove water-soluble impurities, and drying to produce. aluminumoxide powder which was impregnated with aqueous chromic acid solution towhich pre-- cipitated magnesium hydroxide had been added previously. Theother two composites were prepared by methods described in thisspecification involving freezing and thawing of a precipitated aluminahydrogel to break up its gelatinous structure and form powdered materialwhich was Washed more easily than the gelatinous hydrogel to removewater-soluble impurities. In the preparation of the second of theseactive catalysts,

the alumina was "activated by heating the washed material to 950 F.prior to compositing with chromia and magnesia. 7

Each of these three catalyst composites was dried, formed into 3 x 3 mm.cylindrical particles by a pelleting machine, and then calcinedin airfor 10 hours at 1472 F. The catalysts s0 prepared were utilized asfillers in steel tubes through which a commercial butane fraction waspassed at 1112 F. under atmospheric pressure using an hourly gaseousspace velocity of 1500 and a dehydrogenating period with a duration of45 minutes. The commercial butane fraction charged contained 4.3 moleper cent propane, 54.0 per cent isobutane, 40.9 per cent normal butane,and 0.8 per cent pentanes. The results obtained per pass inthe presenceof equal weights of these catalytic materials are given in the followingtable.

TABLE Dehydrogenatz'on of a butane jracttlm in the presence ofalumina-chromia-ma nesia catalysts From the results given in the tame,it is evident that dehydrogenation catalysts prepared from precipitatedhydrogels which have been frozen to break down the gelatinous structureof the hydrogels are superior in dehydrogenating activities to adehydrogenation catalyst of like composition prepared by the moretedious method of the prior art necessary when freezing and thawing arenot utilized in the catalyst preparation procedure.

The character of the present invention and its novelty and utility canbe seen from the preceding specification and numerical data presented,although neither section is intended to. unduly limit its generallybroad scope.

I claim as my invention:

1. A hydrocarbon conversion process which comprises subjecting ahydrocarbon under conversion conditions to contact with a catalystcomprising a componentprepared as a gelatinous hydrogel and whichhydrogel has been subjected to freezing and thawing to destroy itsgelatinous structure.

2. A hydrocarbon conversion process which comprises subjecting ahydrocarbon under conversion conditions to contact with a catalystprepared by forming a hydrogel of a metal oxide,

freezing and then thawing said hydrogel to destroy its gelatinousstructure and to convert it into a finely divided powder, with saidpowder at least one oxide to form a composite catalyst.

3. A process for dehydrogenating an aliphatic and compositing additionalmetal hydrocarbon which comprises subjecting the aliphatic hydrocarbonunder dehydrogenating conditions to contact with a catalyst comprising ametal Oxide component prepared'by forming a hydrogel of a metal oxide,freezing and then thawing the hydrogel to destroy its gelatinousstructure.

4. A process for dehydrogenating an aliphatic hydrocarbon whichcomprises subjecting the aliphatic hydrocarbon under dehydrogenatingconditions to contact with a catalyst prepared by forming a hydrogel ofa metal oxide, freezing and then thawing said hydrogel to destroy itsgelatinous structure and to convert it into a finely divided powder, andcompositing with said powder at least one additional metal oxide to forma composite dehydrogenating catalyst.

5. A process for dehydrogenating an aliphatic hydrocarbon whichcomprises subjecting the aliphatic hydrocarbon under dehydrogenatingconditions to contact with a catalyst prepared by forming a hydrogelselected from the group consisting of aluminum oxide, magnesium oxide,zinc oxide and cadmium oxide, freezing and then thawing said hydrogel todestroy its gelatinous structure and to convert it into a finely dividedpowder, and compositing with said powder at least one additional metaloxide having dehydrogenating activity.

6. A process for dehydrogenating an aliphatic hydrocarbon whichcomprises subjecting the aliphatic hydrocarbon under dehydrogenatingconditions to contact with a catalyst formed by precipitating aluminahydrogel, freezing and then thawing said hydrogel to destroy itsgelatinous structure and to convert it into a finely divided powder, andcompositing with said powder at least one additional metal oxide havingdehydro genating activity.

'7. A process for dehydrogenating an aliphatic hydrocarbon whichcomprises subjecting the allphatic hydrocarbon under dehydrogenatingconditions to contact with a catalyst formed by precipitating aluminahydrogel, freezing and then thawing said hydrogel structure and toconvert it into a finely dividedpowder, and compositing with said powderat least onev metal oxide selected from the group comprising chromia andmagnesia.

8. A'process for dehydrogenating an aliphatic 50 hydrocarbon whichcomprises subjecting the aliphatic hydrocarbon 'under dehydrogenatingconditions to contact with a catalyst formed by precipitating an aluminahydrogel by the addition of a base to an aqueous solution of an aluminum55 to destroy its gelatinous salt selected from the group consisting ofthe chloride, nitrate and sulfate, sufiiciently freezing and thenthawing said hydrogel to destroy its gelatinous structure and to convertit into a substantially amorphous and non-gelatinous powder and anaqueous solution, removing a major proportion of said aqueous solutionfrom said powder, washing the powder to remove water-soluble impurities,and mixing the powder with a solution of a metal compound underconditions to im-' pregnate the powder with the oxide of said metal,heating to remove water, and then drying the composite, and calcining toproduce an active dehydrogenating catalyst.

9. A process for dehydrogenating a paraflinic hydrocarbon whichcomprises subjecting the paraffinic hydrocarbon at a temperature fromabout 750 to about 1400 F. to contact with a catalyst prepared byprecipitating alumina hydrogel, freezing and then thawing said hydrogelto destroy its gelatinous structure and to convert it into a finelydivided powder, and compositing with said powder at least one additionalmetal oxide having dehydrogenating activity.

10. A process for dehydrogenating an olefinic hydrocarbon whichcomprises subjecting the olefinic hydrocarbon at a temperature fromabout 750 to about 1400 F. to contact with a catalyst prepared byprecipitating alumina. hydrogel, freezing and then thawing said hydrogelto destroy its gelatinous structure and to convert it into a finelydivided powder, and compositing with said powder at least one additionalmetal oxide having dehydrogenating activity.

11. A process for dehydrogenating anv arylalkane hydrocarbon whichcomprises subjecting the arylalkane hydrocarbon at a temperature fromabout 750 to about 1400" F. to contact with a catalyst prepared byprecipitating alumina hydrogel, freezing and then thawing said hydrogelto destroy its gelatinous structure and to convert it into a finelydivided powder, and compositing with said powder at least one additionalmetal oxide having dehydrogenating activity.

12. A hydrocarbon conversion process which comprises subjecting ahydrocarbon under conversion conditions to contact with a catalystcomprising at least two components and prepared by forming a gelatinoushydrogel of one of said components,'freezing and then thawing saidhydrogel to destroy its gelatinous structure, and thereafter 7compositing the other of said components with the first-mentionedcomponent.

JOHN F. STURGEON.

